354 GEOLOGY AXD PETROLOGY OF THE GREAT SERPENTIXE BELT OF X.S.W., 



median line, incurved and directed anteriorly. On tbe posterior ear can be seen 

 a sharp fold along the hinge line. The shell is ornamented by simple and inter- 

 polated radial folds spaced eight or ten to a centimetre and travereed by a tew 

 faint concentric undulations. The height of tlie type specimen is 42 mm. ; the 

 height of the umbo above the hinge-line, 14; the breadth, 35, and the thickness of 

 the single valve is 18 mm. 



It was collected by Donald Porter from Swain's Conditional Purchase Lease, 

 seven miles south-east of Carroll, and is in the Museum of the Geological Survey, 

 No. FlSll. 



CONOCARDICII SP. IXDET. 



An indefinite shell which has provisionally been referred to this genus is seen 

 in Specimen No. 4424 in the collection of the Geological Survey, obtained by 

 Cullen from the jjarish of Moorowarra, south of Somerton. 



P0.SIDONIELLA ? spp. INDEX. (Plate xxiii., fig. 6; Text-fig. 14 a, b.) 



Posidoniella, De Koninckj Faune Calc. Carb. Belg., 1885, p. 184. 



These three forms all occur in the south-east of Babbinboon, and were ob- 

 tained by Mrs. Scott. The following features are common in the three shells, 

 which are obviously generically related. The shell has a prominent bean or umbo, 

 incurved and placel subcenti-ally, generally slightly anterior. The hinge line is 

 straight with round angles producing small ears. They are marked with a few 

 (five to eight) prominent ridges, with broad sulci between, in which are seen thin 

 radial striae sometimes extending as spines from, the margin. The two forms, a 

 and h, are rather inflated, but c is much Hatter. The shells are rather like the 

 illustrations of forms of Posidoniella; particularly marked is the resemblance of 

 (a) to Posidoniella suhsulcata* as illustrated by Dr. Wheelton Hind, but they 

 differ from that form in the sub-central character of the umbo and its general 

 prominence above the hinge line. They resemble Atliijris rui/ssii to some extent, are 

 the possessors of a lamellar fringe as shown in b (which is the only bilaterally 

 symmetrical form), but differ from it in the presence of so few concentric ridges, 

 and usually asjTnmetric character and anterior inclination of the umbo Tenta- 

 tively, however, the^e forms have been assigned to the genus Posidoniella, awaiting 

 the investigation of further material. 



The following are the characters of the three forms : — 



(n). This is the form illustrated in Text-flg 14a, and two specimens of it are 

 available. The following are tbe dimensions of this form: — Heiglit, umbo to 

 margin, 13, 14 mm. ; length, 11, 12 mm. ; length of hinge line, 9 nun. ; height of 

 umbo above hinge, 4 mm.; thickness of valve, (i ram.; iiumbei' of coiiceiili-ic folds, 

 7—8. 



The beak in both cases is not quite central, and tlie middle line is very slightly 

 obli(|ue to the normal to the hinge line. The ears, liowever, are very nearly eiiual 

 and the hinge line is straight. The radiating striae are marked. 



(b) . This also is represented by two specimens, and is proportionately broader 

 than the first. The following are the chief diniensions of the two specimens: — 

 Height, 6.5, 6.2 mm.; length, 8, 7.2; length of hinge-line, 5. 4.5; height of umbo 

 above hinge-line. 2.5. 2.5; thickness of valve, 3.7, 3.5. 



In both there were five marked concentric lolds with intervening fhie railial 

 markings, which are continued into a fringe along the margin of one of these 



•Brit. Carb. LameU., II. (iii.), 1904, t.25, f.2-6. 



